(CNN) – At least three people were killed in Venezuela when clashes broke out during anti-government protests described by opposition leaders as the “mother of all marches.”

Supporters of President Nicolas Maduro also held a counter rally Wednesday as opposition marchers gathered in the streets.

An hour into the march in Caracas, a 17-year-old boy was shot in the head, according to the Venezuela’s public ministry, which said it had started investigating the incident. The teenager, later identified as Carlos Moreno, died while undergoing surgery, a hospital representative told CNN.

Moreno’s sister, Alejandra, said Carlos studied economics at Venezuelan Central University in Caracas. Instead of joining the marches, she said, he was on the way to play soccer.

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